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Vincent Rouilly from OpenWetWare.org is using Contraptor plotter to build an open source robot for microbiology lab. Needless to say, I am pretty excited about this! We've been exchanging emails, modding Arduino GCode Interpreter and figuring out how to drive a plotter head with a cheap servo. He made a great suggestion to use different colors for different components in Sketchup files. Up till now, the 3D model of a contraption would be pretty much required to look at during assembly. With components in color, assembly from Sketchup screenshots (or printed pages) is a whole lot easier.

To investigate the plotter stalling problems that were encountered during recent tests, I had ordered Keling stepper motors - one of the official choices of the Reprap project. They are rated for 166 oz*in of holding torque (vs 60 oz*in in Alltronics). They also cost about as much more. When the Keling steppers arrived, I assembled the plotter again. 

For some reason, the maximum feedrate that Keling steppers gave without stalling was 300 IPM, and that was on single-axis movements (like "G1 X10" or "G1 Y6"). Alltronics steppers could do about 600 IPM on single-axis movements in previous tests. I thought this was strange and decided to install Alltronics back to compare.

After I modified the XY plotter design to use new linear motion components, increasing the work area along the way, I needed to actually assemble and test it. During the build, I had to add a couple of shaft mounts with bearings, supporting the middle section of the threaded rods - they were bending too much. These changes are reflected in Sketchup files for the XY plotter. I also used version 1.2 of stepper motor driver boards. The good thing is that SMD v1.2 uses IDC header with 10-pin ribbon cable for Arduino interface as opposed to CAT5 in SMD v1.1 (which is soldered directly to the board and can break from bending). Unfortunately there is only 8 inches of the ribbon cable included with the SMD v1.2 kit, so I was constrained in where I can place the SMD boards and Arduino. This resulted in the weird "Γ" arrangement of heatsinks, as seen in the pics.

I finally updated the plotter design to use new linear motion components. While at it, I moved few things around, like belts to the outside; and now the plotter has 17"x11" work area. I have not assembled/tested it yet, but I think most parameters from the older version still apply. The BoM is also compete ($290 if built from scratch), the files are at http://contraptor.svn.sourceforge.net/viewvc/contraptor/trunk/contraptions/xy-plotter/

I worked on the plotter contraption pretty much every evening during the last couple of weeks, and here is the result of all that tinkering. I had reservations about several things - I thought it would be too difficult for the motor to move the X stage around at the max speed (150rpm) - not so. To connect the opposite pulleys of the Y stage, I used 17" lengths of 1/4" all-thread rod coupled to 10-24 rod ends - and I thought it would bend too much making the belts too loose. It does bend a bit but the belts seem to be fine.